U.S. Pat. No. 4,729,717, assigned to the assignee hereof, discloses and electric-motor in-line hydraulic pump assembly that includes a stationary shaft disposed within a housing. A pair of spaced cylinder blocks are counter rotatably mounted on the shaft, and arrays of pistons are carried within each of the cylinder blocks and engage opposite side of a common yoke plate. Synchronous or asynchronous (induction) motor stators are positioned within the housing and surround rotors mounted on the cylinder blocks. A controller energizes the respective motors so that the cylinder blocks rotate in opposite directions and can be held 180.degree. out of phase with each other. A yoke plate control piston and pressure compensator valve are carried by the housing and coupled to the pump fluid output for maintaining constant output pressure and destroking the pump when fluid output pressure exceeds the desired level.
U.S. application Ser. No. 07/412,211 filed Sep. 25, 1989, now U.S. Pat. No. 5,073,091 likewise assigned to the assignee hereof, discloses a variable displacement hydraulic pump that includes a housing and a rotatable shaft that projects from the housing for external connection to a motor or other source of motive power. A cylinder block is coupled to the shaft for corotation with the shaft within the housing, and includes a plurality of cylinders disposed in a circumferential array parallel to and surrounding the axis of the shaft. A piston is disposed to reciprocate within each of the cylinders, and is coupled to a yoke plate for determining displacement of the pistons within the cylinders. A valve plate is mounted on a valve block and includes kidney-shaped slots for registering with the cylinders as the cylinder block rotates, and thereby connecting the cylinders to pump inlet and outlet ports. A microprocessor-based controller is externally mounted on the pump valve block, and includes internal memory having various remotely-selectable control programs prestored therein. Sensors responsive to pump operating conditions are connected to the pump controller, and include a first sensor responsive to yoke plate position as variable controlled by the controller, a pressure sensor responsive to pump output pressure, and a speed sensor responsive to angular velocity of rotation of the shaft and cylinder block. Preferably, all of the electric components are mounted on the valve block.
A general object of the present invention is to provide an electric-motor hydraulic pump of the type disclosed in the above-noted patent that includes facility for enhanced control of pump output fluid pressure and flow. Another and more specific object of the present invention is to provide an electric-motor hydraulic pump of the described character in which effective pump displacement and speed are controlled electronically by modulating the output of the electric motor, rather then hydro-mechanically as is typical of the prior art, so as to reduce power consumption . Yet another object of the present invention is to provide an electric-motor hydraulic pump having improved response to changing output commands and/or conditions.